The present invention relates generally to the field of air filtration and purification and, more particularly, to a complete onsite chemistry air filtration system that enables reactant chemistries to be dynamically generated, contained and controlled onsite for the purpose of removing undesirable contaminants from air. The present invention synthesizes multiple technologies to achieve this end.
Airborne particulate filtration has existed for perhaps hundreds of years with the goal of removing solid particulates from air, typically using a filter comprising a fine web of porous media through which the solid particulates cannot pass, yet gaseous molecules can pass. The size of the pores in the filter media determines the efficiency of the filter (efficiency in this case referring to the maximum sized particulate that may pass through the filter). Such filters sometimes are charged or enhanced with an electrostatic field to increase particulate removal efficiency without reducing media pore size, which would undesirably increase the gas flow pressure drop across the media. Nevertheless, such filters still allow gases to pass through.
Gas phase filtration was introduced in the 1960s to remove gases from the airstream using dry media. In gas phase filtration systems, media is selected to suit the particular contaminant(s) and is usually carbon- or alumina-based. Media may be activated through processing treatments and may be impregnated with additional chemistry to increase capacity and selectiveness of removal.
Most current commercial gas phase filtration applications use either carbon or alumina impregnated with potassium permanganate. Carbon acts by attracting and loosely holding undesirable airborne chemicals. Permanganate impregnated alumina acts as an oxidation media and chemically changes contaminant gases to more stable molecules of their component parts.
However, some chemicals, such as ammonia, require reduction chemistry for removal and, therefore, such chemicals typically have been ignored by prior art filtration systems due to the fact that a completely separate stage of media would be required. Additionally, the capacity for impregnated and activated static media is finite and presents a time-consuming and expensive limitation to the prior art.
In gas phase filtration systems, a certain amount of residence time (the time the gas is exposed to the filtration media) is required, and once the reactive media depth is reduced, residence time also may be reduced below an acceptable figure, resulting in gas bypass and breakthrough. Thus, once the filtration media has been reacted or saturated, the removal efficiency of the filtration system drops significantly. In order to maintain high removal efficiency rates, it is necessary to discard a substantial amount of media, which may be only marginally used. Discarding media that is only partially used unnecessarily increases costs.
Ultraviolet (“UV”) light in selective wavelengths has been found to have favorable properties in air filtration. For example, in certain wavelengths it can act destructively on thymine in microorganism DNA, thus preventing replication. Radiation also can be absorbed by molecules “in transit” through an air filtration system, creating energized state where chemical reactions are far more likely to occur. Several paths are possible for a return to a less active state.
Further, in photochemical reactions, UV radiation (generally less than 385 nm) absorbed on the surface of a photocatalytic material generates highly reactive electrons and holes. Photocatalytic adsorbates with suitable redox potentials undergo electron transfer processes at the material surface. For example, UV radiation promotes electrons from the valence band into the conduction band of a titanium dioxide semiconductor photocatalytic material. In an air filtration context, destruction of volatile organic compounds (“VOCs”) takes place through reactions with molecular oxygen or through reactions with hydroxyl radicals and super-oxide ions formed after the initial production of highly reactive electron and hole pairs.
Additionally, and quite importantly in the present invention, UV light in the vacuum-ultraviolet (“VUV”) range (less than 200 nm) also generates ozone and almost completely breaks down water molecules to H and OH. The latter hydroxyl radical is one of the most powerful oxidizing agents known with an E°=+2.7 v in acid solution.
The onsite chemistry air filtration system of the present invention marries and synthesizes a number air technologies to create the unique synergistic effect—a single, complete air filtration system that uses complementary chemical processes to dynamically generate, contain and control reactant chemistries. No air filtration system known in the prior art offers such a complete system.
Accordingly, there exists a need for an improved air filtration system to overcome the limitations found in the prior art and to create a nearly self-sustaining device. Desirably, the air filtration system is configured to advantageously combine a series of air filtration methods and technologies in sequence for filtering a wide array of gaseous contaminants. More desirably, the air filtration methods and technologies in such a system complement one another to dynamically generate, contain and control the reactant chemistries of the air filtration methods and technologies. Most desirably, such a system may be easily installed and retrofit into existing air handling systems.